In general, the seats of a vehicle should be mounted in a limited space of the vehicle and in a limited weight range for supporting passengers safely and pleasantly. Therefore, a seat back includes a seat back frame and a seat back pad for supporting the waist and back of a driver or a passenger, and a driver who sits in the driver's seat or a passenger who sits in a passenger's seat beside the driver's seat pulls forwards or pushes backwards the seat back according to driving habits and body conditions by means of a rotation device of the seat, thereby controlling the angle of the seat back.
In particular, it is difficult to essentially correspond to the change in the seating posture of the driver or the passenger by just the seat back frame and the seat back pad in the case of long time driving. Therefore, a buffering device and a lumbar support are mounted in the seat back for comfortably surrounding the back of the driver or the passenger and comfortably supporting the lumbar vertebra.
Even though it is possible to change the bending degree of such a conventional lumbar support by manual adjustment of a rotary lever which is mounted to a side wall portion of the seat, there are demands to provide the convenience of the driver or the passenger in any other way rather than the manual adjustment.